Method for the extraction of aleurone from bran

ABSTRACT

The invention relates to a method for the preparation of aleurone from bran, in particular, wheat bran, for the extraction of aleuronic cells in particular from wheat grain, whereby the mainly aleurone-containing aleuronic components are separated from the mainly non-aleurone-containing non-aleuronic components in the bran and the aleurone-containing components are then isolated. The separation can be achieved by biochemical/enzymatic means and/or by mechanical-abrasive means. The subsequent isolation and extraction can be achieved by wet and/or dry separating methods.

The invention relates to a method for processing bran, in particularwheat bran, and extracting aleurone cells, in particular those of wheatkernels. Furthermore, it relates to the use of the separated or isolatedaleurone components as an additive to foodstuffs and feedstock, or as afood supplement or feed supplement. In addition, it relates toaleurone-containing products and in particular to aleurone-containingfunctional food.

A wheat kernel can be divided into three primary components, namely thehull (or “bran”), endosperm, and germ. The hull itself consists ofseveral finely differentiated layers, which may also be classified inthree groups:

-   -   Pericarp (epidermis, longitudinal cells, cross cells, tube        cells)    -   Seed coat or testa (pigmented layer, colorless layer)    -   Aleurone layer

The aleurone cell layer of wheat is a single-row layer consisting ofthick-walled cells, the contents of which are very important from anutritional and physiological perspective. The aleurone cells containvitamins, minerals, fats, protein, phosphorous, and fibers (cell wall),among other things. The aleurone layer is the outermost boundary layerof the endosperm, and it is thus botanically part of the endosperm andnot the hull. The cohesion between the aleurone cell layer, the verythin hyaline layer, and the seed coat due to very strong adhesive forcesis particularly evident during mechanical separation of the endospermand hull (“cleaning the bran”). Thus from a milling standpoint, thealeurone cell layer is part of the bran or hull, which may later be usedas bran for eating or feedstock.

The endosperm of a cereal grain and in particular of a kernel of wheatis surrounded by multi-layered hulls. The pericarp is located on theexterior, consisting of the epidermis, cross cells, and tube cells.Moving inward toward the endosperm, next comes the seed coat, followedby the nutritionally and physiologically important aleurone cells aftera hyaline layer. These aleurone cells contain many minerals, vitamins,and fibers, and they are adulterated with very few contaminants becausethey are protected by the pericarp and seed coat.

Although the pericarp can be separated from the seed coat relativelyeasily, it is very complicated to separate the aleurone cells from theseed coat. Therefore, the entire batch of bran is usually allocated foruse as feedstock or bran for eating. Hydrothermal stabilization isperformed according to DE-A-4435453 in order to obtain storable bran forthis purpose.

It is also a well-known method to produce oxidation-resistant rice branaccording to Japanese publication number 11103803 by extracting the branfrom steeping water after the rice is processed (“rice polishing”). Forthis purpose, an agent is first added to the steeping water, and thewater is subsequently removed by thermal treatment. This formsrelatively large bran particles at the same time. Bran is also obtainedwhole with this method.

U.S. Pat. No. 5,082,680 describes a costly mechanical method for thelayer-by-layer separation of bran. With this method, the bran is removedlayer-by-layer by using four polishing or scouring steps and a scrubbingstage with two wettings. After the first wetting of the cleaned, drywheat, it is allowed to stand. The epidermis is then removed from thepericarp during the first polishing stage.

After the second wetting, cross cells and tube cells are removed fromthe pericarp during the second polishing stage. These bran layers aresifted to separate the germs from the ground grain. Due to their assumedlow levels of phytate phosphorous content, these sifted bran layersshould be used as a food additive.

In the third polishing stage, the seed coat, portions of the hyalinelayer, and aleurone cells are removed.

In addition to any remaining seed coat, the fourth polishing stagespecifically removes the aleurone layer, which is no longer consideredworth processing.

During final scrubbing, the bran residue which is still adhering and thegerms are removed, followed by cooling and wetting; it is then allowedto stand.

This prior art certainly hints at a partial use of bran; however, itdoes not offer any solution for the specific removal and use of aleuronecells.

The underlying problem of the invention is to avoid the indicateddisadvantages of the prior art and to extract the physiologically highlyvaluable aleurone components, in particular those of wheat kernels, fromthe bran containing them in the most complete and careful mannerpossible.

An additional problem is to make the aleurone components extracted inthis manner specifically suited for addition to and to add them to humanand animal food.

These problems are solved by separating the predominantlyaleurone-containing aleurone components from the predominantlyaleurone-free non-aleurone components and subsequently removing thealeurone-containing components. The removed aleurone components are thenadded to conventional foodstuffs as an additive or as a separatesupplement.

The bran can be removed with biochemical enzymatic processes, mechanicalabrasive processes, or by any combination of biochemical enzymatic andmechanical abrasive treatment.

During biochemical enzymatic treatment, the bran is kept in a containerfilled with water at an optimal temperature and an optimal pH value forenzymes. A biochemically active substance containing enzymes is added sothat the adhesive forces between the aleurone cell layer and the brownseed coat are weakened by the enzymes in such a way that the aleuronetissues can easily be separated from the seed coat undamaged by means ofa mild mechanical action.

It is expedient for the bran first to be reduced to a size of 400-800μm, which will preferably free the bran of any endosperm still adheringto it.

The aleurone tissues will preferably be separated from the seed coatundamaged by means of a mild mechanical action. It is convenient if themechanical action is applied to the bran in the form of active shearingforces. For example, this may be accomplished by directing the liquid inwhich the bran is being kept into a colloid mill, by which the shearingforces are then applied. The mechanical action may also be applied bymeans of an extruder.

In one particularly preferred embodiment, the cell walls of the aleuronecells are at least partially ruptured by the biochemical substance sothat the contents of the aleurone cells can escape. More or lesscomplete enzymatic degradation of the aleurone cell walls may bepreferred for nutritional and physiological reasons, as required. Thesecell walls are hemicellulose, which is an important necessary element oflife for certain intestinal bacteria.

Surprisingly, it has been shown that an aleurone layer and itsindividual cells can be separated from the firmly adhering seed coat byweakening their adhesion. This is preferably accomplished by means ofsuitable enzymes; for example, endoxylanase/arabinoxylanase. Rinsing incold water promotes the weakening of the adhesive bond.

Aggregates of aleurone cells with intact cell walls or cells in solutionare obtained, the contents of which can be separated and degraded.

The enzymes to be used are also quite safe for human food, so thealeurone cells or their contents (proteins, vitamins, etc.) inparticular may be used for or in dietary foodstuffs.

It has been shown that the adhesive forces between the aleurone cellsand the quite tenacious brown seed coat can be neutralized by the use ofenzymes and mild mechanical impaction, thus resulting in the release ofintact aleurone cells from the seed coat.

This is accomplished primarily by enzymes with xylanase action and mildmechanical impaction by means of a centrifugal mill.

In addition, it has been shown that the aleurone cells can be completelydissolved by treating bran with enzymes; thus, it is possible toseparate the aleurone cell contents and their cell wall fragments fromthe hull components situated above them which remain undamaged, inparticular those of the seed coat. This is primarily done with an enzymemixture of xylanase, betaglucanase, cellulose, and arabinase.

SUMMARY

Either intact or degraded aleurone cells or their contents are obtainedunder the appropriate conditions.

The enzymes used are quite safe for human food.

An additional advantage is provided by the possibility of analyticalaccess to individual layers.

It is expedient for predominantly aleurone-containing components andpredominantly aleurone-free components of the bran located in thehydrated mixture to be separated or isolated from one another.

This separation or isolation can be accomplished with the “wet” versionof the invented method, whereby the hydrated mixture of enzymaticallytreated bran is pressed, so that dissolved and suspended aleuronecomponents are carried in the hydrated phase as aleurone juice, and theremaining bran components remain in the press as press cake.Alternatively, the hydrated mixture of enzymatically treated bran can befiltered, so that dissolved and/or suspended aleurone components arecarried in the hydrated phase as aleurone juice, and the remaining brancomponents remain in the filter as filter residue.

However, the hydrated mixture of enzymatically treated bran can also beseparated into the aleurone components and the non-aleurone componentsby decanting. Or they can be separated in two non-mixable liquids intothe aleurone components and the non-aleurone components due todifferences in wettability and/or differences in solubility. In somecases, it is also possible and quite convenient to perform theseparation or isolation by a combination of the aforementionedseparation steps. Both the same and different separation steps can beperformed in sequence on the same hydrated mixture.

To separate or isolate the different aleurone components from oneanother, the aleurone juice in which the aleurone components are carriedwill preferably be centrifuged. The aleurone juice can also be filteredby microfiltration and/or ultrafiltration for this purpose. It can evenbe subjected to reverse osmosis in order to separate or isolateadditional specific aleurone components. In this manner, differentfractions of aleurone components can be extracted which can bespecifically used in functional food.

Water will preferably be extracted from the aleurone juice in which thealeurone components are carried in order to increase the concentrationof aleurone components, so that concentrated aleurone juice isextracted. Alternatively, an aleurone powder consisting of aleuronecomponents can be produced by spray drying, freeze drying, or vacuumdrying. Pre-concentration will preferably be carried out in anevaporator before producing the aleurone powder. In particular,dissolved proteins are precipitated in the aleurone juice by heating thealeurone juice or by salting out the proteins. The aleurone-containingproducts extracted in this way can be handled quite easily.

In order to obtain a product which does not alter its properties andwhich keeps well, the hydrated mixture or the aleurone juice, whichcontains the aleurone components and the biochemically active substancewith the enzymes, is pasteurized after a sufficiently long period ofenzymatic activity before concentration or pulverization.

In the “dry” version of the mechanical abrasive treatment of the bran,the aleurone components are separated from the non-aleurone componentsin a rolling mill, a centrifugal impact mill, or a jet mill. Thesemethods can also be combined, if required. It is expedient for the branto be moistened before it is subjected to mechanical abrasive treatment.

In one particularly convenient embodiment of the invented method, i.e.the “wet” version of the mechanical abrasive treatment, the bran isadded to water and the aleurone components are separated from thenon-aleurone components in a colloid mill or in a ball mill in whichplastic balls of the same thickness as the bran will preferably be used.

The aleurone components and non-aleurone components separated from oneanother in the dry or the wet method are graded and sorted intofractions. The grading and sorting of the mixture of aleurone componentsand non-aleurone components can also be performed by air-classification,if necessary after prior drying. It is preferable to use a channelimpeller air-classifier, a zigzag air-classifier, or a cross-flowair-classifier for this purpose. Combinations of these types ofair-classifiers can also be used here, if required.

In another convenient embodiment, the fine particles of a fine fractionextracted by air-classification are removed before they are subjected toadditional grading by sieving.

This prevents the sieves from becoming plugged by the buildup of fineparticles on them. Grounded metallic sieves will preferably be used forsieving. This will reduce the risk of the fine particles becomingcharged and an agglomeration of these fine particles forming. In anynecessary additional steps for separation or isolation, suchagglomerations of fine particles would produce adulterated fractions.

Following grading or sorting by air-classification, there is grading orsorting in an electrical field, if required. Both spatially homogenousand heterogeneous, temporally constant fields and alternating fields canbe used. This allows different particles to be separated from oneanother due to their different electrical charges and/or their differentelectrical polarization.

For example, if a channel impeller air-classifier is used to process thewheat bran, whereby the different particles of the coarse fraction ofthe bran, which contains both non-aleurone hull particles originating inthe furrow of the wheat kernel and aleurone particles, are electricallycharged and/or polarized due to static electricity in various waysduring their passage through the arched or in particular the circularchannel of the channel impeller air-classifier because of the particlesrubbing against one another and/or the channel wall and they follow apath through an area subjected to an electrical field after leaving thechannel impeller air-classifier, this allows the collection of thenon-aleurone hull particles originating in the furrow at one spot andthe collection of the aleurone particles at a second spot different fromthe first spot. This separation is particularly convenient, because thismakes the white to yellowish aleurone particles released from the darkhull particles of the furrow look cleaner visually. Furthermore, itshould be mentioned that the furrow of wheat kernels can only be poorlycleaned, if at all, so it contains many unwanted substances and perhapseven environmental toxins.

In another embodiment, the mill product consisting of ground bran isseparated by simultaneously directing the mill product into an inclined,vibrating channel at one spot, whose inclination, surface roughness, andvibration are designed in such a way that the different mill productcomponents move along the channel at different migration speeds, whichallows different mill product fractions with more or fewer aleuronecomponents to be extracted at different spots further along the channelat successive time intervals.

However, it is preferable for the separation of the mill productconsisting of the ground bran by means of the channel to be performed bysimultaneously directing the mill product into an inclined, vibratingchannel at one spot, whose inclination, surface roughness, and vibrationare designed in such a way that the aleurone components migrate to theupper end of the channel while the non-aleurone components migrate tothe lower end of the channel.

Another possibility for separating the mill product is sedimentation ina fluid-filled container, whereby different mill product fractions areextracted at the bottom of the container as sediment layers containingmore or fewer aleurone components due to the differing sinking times ofthe various mill product components in the fluid-filled container.

The mill product can also be separated by moving the mill productparticles along an equipotential surface of a heterogeneous electricalfield, which causes the mill jet or the mill stream to be split intofractions containing more or fewer aleurone components due to thediffering dielectric properties of the mill product particles. Forexample, the jet of mill product particles can be moved by means of alaminar-flow carrier fluid flowing through an equipotential surface ofthe electrical field in a defined path and thereby be split by theheterogeneous electrical field.

It is expedient for the mill product particles to becomeelectrostatically charged by rubbing against one another and/or on partof the container and then moved transversely to an electrical field,which causes the mill jet or the mill stream to be split into fractionscontaining more or fewer aleurone components due to the differingelectrical properties of the mill product particles. In particular, thejet of mill product particles is moved in a defined path by means of alaminar-flow carrier fluid flowing transversely to the electrical fieldand is then split by the electrical field.

Separation can also be accomplished by a combination of theaforementioned separation steps, whereby there is preferably only oneswitch from the “wet” method to the “dry” method.

After the fractionation of the bran components, e.g. by means of one ofthe aforementioned methods, the mill product fractions extracted can befurther treated with a biochemical substance specific to each fraction.This allows the properties of the product to be specifically influenced.Therefore, it is quite reasonable first to isolate the differentaleurone fractions from one another, then treat each fraction in aspecific manner, and then to remix the specifically treated fractions.This makes it possible to alter the relative concentrations of themixture prescribed by nature, which is important for the production offunctional food.

The biochemical substance will preferably contain at least one of theenzymes betaglucanase, cellulose, xylanase, and arabinase in a hydratedmedium with which the mill product fractions are mixed into a hydratedmixture.

It is particularly convenient if the biochemical substance contains atleast one of the enzymes endoxylanase, beta-xylosidase,arabinofuranosidase, acetylesterase, xyloacetylesterase, and feruloylesterase in this hydrated medium with which the mill product fractionsare mixed.

It is preferable for the aleurone base of the food supplement or feedsupplement to be in the form of a pressed pellet of aleurone componentsand a nutritionally and physiologically harmless binding agent. Forexample, the aleurone powder described above may be used in thisproduction process.

The food supplement or feed supplement can also be in the form of adrink. The aforementioned concentrated aleurone juice, for example, maybe used for this in a more or less concentrated form.

The additive or the food supplement or feed supplement can also be apowder. The aleurone powder described above may also be used for thispurpose.

In addition, the foodstuff can be a starchy product or a dairy product.In principle, however, the aleurone-containing additive can be added toany desired processed food as a powder or as juice in order to producefunctional food with a special physiological effect, special taste,special texture, etc.

Thus, a form of aleurone components isolated by specific microfiltrationand/or specific centrifugation from the protoplasm of aleurone cells,for example, can be added to the functional food. A portion or all ofthe above-mentioned separated or isolated aleurone components may alsobe contained in the aleurone-containing product.

The invented functional food contains at least one of the substancescontained in the aleurone extracted according to the methods describedabove.

The invented functional food may optionally contain aleurone cells whichhave been fully hydrolyzed by enzymatic action or aleurone cells whichare still completely intact. The cell walls and cell contents of the“quasi-predigested” fully hydrolyzed aleurone cells can thus be applieddirectly to human metabolism. At the same time, the enzymaticallypartially hydrolyzed and thus “half predigested” aleurone cells withtheir “weakened” cell walls will be more easily digestible for humans onthe one hand, but they will still be able to serve as food forintestinal bacteria on the other hand. Even the proportion of completelyintact aleurone cells in this type of functional food will do a humanbeing good, since the hemicellulose cell walls of the aleurone cells canbe digested by human beings, at least with the cooperation of intestinalbacteria.

Additional benefits, features, and potential applications of theinvention may be seen in the following description of some exemplaryembodiments which are to be interpreted not to exclude otherembodiments.

Wet Method:

Dry, cleaned wheat is stirred in a closed container filled with watermixed with enzymes.

The water is heated by the addition of the mechanical energy, or thetank may be equipped with a separate heating device to accelerate theheating process.

The pericarps are removed by the action of the enzymes and may beseparated. After additional stirring, the seed coat also separates fromthe aleurone cells, which separate from the endosperm. The endospermscan now be removed and the aleurone cells in the water can be degradedseparately.

EXAMPLE 1

Wheat bran with a size distribution of 400-8000μ is mixed with water andstirred at a temperature of 45-55° C., and an enzyme solution (xylanase,betaglucanase, cellulose, and arabinase) is added. Due to the action ofindividual or multiple enzymes, the aleurone cells can first beseparated from the seed coat as tissue, and then be completely dissolvedand thus sieved off of the remaining hull components. The aleurone cellsare thereby dissolved, and the cell contents pour into the solution asprotoplasm. The wet sieve residue contains the non-dissolved hullcomponents (seed coats, pericarps). The wet sieved material contains thecontents of the aleurone cells and their cell wall fragments.

This wet sieved material is concentrated into a yellowish-gray powder byspray drying and/or freeze drying.

EXAMPLE 2

Wheat bran with a size distribution of 400-800μ is mixed with water andstirred at a temperature of 45-55° C., and an enzyme solution (xylanase)is added. This causes weakening of the adhesive forces between the seedcoat and the aleurone cell layer, resulting in the separation of the twolayers adhering to one another. This effect can be optimized by mildmechanical action (centrifugal mill) without disrupting the tissues.

EXAMPLE 3

Wheat bran is mixed with water and stirred for an hour at a temperatureof 45-50° C., and an enzyme solution (xylanase, betaglucanase,cellulose, and arabinase) is added. The remaining suspension is dividedby a disperser for two minutes. The suspension which is left after thisis sieved. The wet sieved material contains the degraded aleurone cellsand their contents, while the sieve residue consists of seed coat whichis completely free of aleurone cells.

Dry Method:

After cleaning in the bran centrifuge, the accumulated bran is dried andslightly heated. After being ground in a mill, where the actualseparating action between the hull and aleurone layer should takeeffect, the mixture of bran components is sieved into fractions. It isthen air-classified to sort the components of the hull (pericarp, testa)and aleurone with any adhering hull components. The separation, sieving,and sifting steps will naturally be repeated multiple times to obtainthe desired level of enrichment of aleurone cells. The aleuronecomponents obtained contain a concentration of at least 60% aleuronecells, and preferably more than 80%. Depending on their use, thesecomponents are further dried and ground, e.g. on a roller mill. Theindividual steps are described in greater detail below.

During the separation stage, the bran particles must be subjected toforces which cause the aleurone and hull to separate. If an impact millis used, the pieces are substantially bent as a result of the forcesapplied (impact force, weight forces). With particle sizes ofapproximately >800 μm, this results in the pieces being fragmented andnot separated. Only if the pieces fall below a certain size can thealeurone and hull definitely be separated by the action of the weightforces. The size of the particles at which separation occurs depends onthe strength of the various layers (pericarp cellulose; testahemicellulose; aleurone→hemicellulose) and the adhesive forces beneaththe layers. Strength and adhesive force are significantly affected bymoisture and temperature. For optimal separation conditions, the branmust first be thermally treated. Tests have shown that a productmoisture between 8%-12%, preferably 10%, is optimal. In this case, theproduct temperature should not fall below 25 C. during separation.

Impact mill speeds of approximately 70 m/s (but <120 m/s) have proven tobe beneficial. The sieve used should have a mesh size of 0.3-0.8 mm,preferably 0.5 mm. So-called “raffle” sieves (brand name Conidur) with0.5 mm meshing produced good results.

In addition to impact forces, collision forces such as those occurringin a jet mill or a centrifugal impact mill have proven to be beneficial.The operations in a centrifugal impact mill (MIPS) are shown to have abeneficial effect on separation, because the flaky bran particles arelined up by the guide blade in the centrifuge rotor and the impactoccurs on the edge. This allows weight forces to take effect withoutcausing any bending stress to be applied to the particles and thuswithout fragmentation. This causes the hull and aleurone to be separatedas larger pieces, and thus simpler devices can be used for sorting.

Thus, the method for extracting aleurone can be subdivided into 5 steps:

-   -   1. Drying/Heating    -   2. Separation    -   3. Sieving    -   4. Air-Classification (Sifting)    -   5. Fragmentation

Experience shows that a bran particle goes through several cycles afterdrying. The number of cycles greatly depends on the desired quality(hull proportion). Particles which are part of the >500 μm fractionduring sieving after the separation stage are directed back to theseparation stage again, because the testa generally has not fullyseparated from the aleurone in this fraction. Depending on the desiredquality, it must go through sieving and air-classification multipletimes. Experience shows that particles >300 μm can be optimally sortedwith a zigzag air-classifier. Particles <300 μm show a tendency toagglomerate, which suggests the channel impeller air-classifier. Thistype of sifter has the advantage of dispersing the agglomerations, andit also has a greater separating capacity.

As is well-known, fraction width and separating capacity play animportant role in sorting. Tests have shown that favorable sievefractions can be extracted for the subsequent air-classifiers by usingthe following mesh widths for sieving:

1. 400 μm

2. 300 μm

3. 200 μm

4. 150 μm

5. 100 μm

Measurements of the most important minerals (Ca, Fe, K, Mg, P, Zn) haveshown that the bran may be enriched by a factor of 2, and thus theproportion of hull components must be <10%. This is only inapplicable tothe fraction which accumulates as sieved material (100 μm sieve). It isnaturally quite difficult and thus costly to sort particles of this size(<100 μm).

If the intended use so requires, the aleurone cells may be broken upwith a roller mill in a final step.

Chemical Analysis of Aleurone Extracted with the Applicant's MethodSubstance Mass Content Content per 100 g Energy (estimated) kcal/kJ2001/840 Protein g 16 Carbohydrates g 42 Starch g 1 Cellulose g 0 ofthis, sugars g 12.9 Free sugars g 8.6 Raffinose g 2.6 of this, fat g 8Saturated fatty acids g 1.4 Monounsaturated fatty acids g 1.4Polyunsaturated fatty acids g 5.2 of this, edible fiber g 45 Soluble g15 Insoluble g 30 Vitamins E (tocopherol) mg 6 B1 (thiamin, aneurin) mg1.3 B2 (riboflavin, lactoflavin) mg 1 B6 (pyridoxine, adermine) mg 4Folic acid g 300 Niacin, nicotine amide mg 35 Pantothen acid mg 4.5Minerals (Ash) Calcium (Ca) mg 2,225 Magnesium (Mg) mg 915 Phosphorous(P) mg 2,520 Iron (Fe) mg 22 Zinc (Zn) mg 28 Phytochemicals Phytic acidg 4.12 Ferulic acid mg 5 Caffeic acid mg 1 Chlorogenic acid mg 1 Lignansg 13 Arabinoxylan g 29

The table shows the results of a chemical analysis of aleurone extractedwith the invented method performed by the applicant.

The notable improvement of many body functions due to aleuroneenrichment in food should be particularly emphasized. For example,polyunsaturated fatty acids have a positive effect on theheart/circulatory system and on cholesterol levels. Vitamin E(tocopherol) has a positive effect on the heart/circulatory system andcholesterol levels, as well as the colon. Vitamin B6 (pyridoxine,adermine) has a particularly positive effect on general health andwell-being. Like magnesium, folic acid has an extremely positive effecton mental and physical performance. Iron also contributes to one'scondition of general health and well-being. Both soluble and insolubleedible fibers have a very positive effect on digestion, theheart/circulatory system, and the colon.

1. Method for processing bran and extracting aleurone cells, wherein thealeurone-containing aleurone components are separated from thealeurone-free non-aleurone components in the bran, and thealeurone-containing components are then removed, and wherein thealeurone-containing aleurone components are separated from thealeurone-free non-aleurone components by a mechanical force selectedfrom the group consisting of impact forces, collision forces andcombinations thereof, and wherein a fraction comprising the aleuronecomponents and non-aleurone components separated from one another andhaving particle sizes above 100 μm are graded and sorted into fractionsby channel impeller air-classification.
 2. Method according to claim 1,wherein the bran is first fragmented to a bran fragment size of about400-800 μm.
 3. Method according to claim 1, wherein the bran is firstfreed of endosperm.
 4. Method according to claim 1, wherein grading orsorting is performed by a combination of channel impellerair-classification and at least one of zigzag air-classification andcross-flow air classification.
 5. Method according to claim 1, whereinthere is grading or sorting in an electrical field following grading orsorting by air-classification.
 6. Method according to claim 1, whereinthe bran is wheat bran and the aleurone cells are those of wheatkernels.
 7. Method according to claim 1, wherein separation is carriedout in an impact mill operating at a speed in the range of approximately70 m/s to <120 m/s.
 8. Method according to claim 1, wherein separationis carried out such that no bending stress is applied to the bran whileweight forces take effect on the bran.
 9. The method according to claim1, wherein the fraction comprising the aleurone components andnon-aleurone components which is sorted into fractions by channelimpeller air-classification has particle sizes above 100 μm and lessthan 300 μm.
 10. Method according to claim 1, wherein the fine particlesof a fine fraction extracted by air-classification are removed beforethey are subjected to additional grading by sieving.
 11. Methodaccording to claim 10, wherein grounded metallic sieves are used forsieving.
 12. Method according to claim 1, wherein moisture andtemperature during separation are controlled so as to allow optimalseparation conditions.
 13. Method according to claim 12, wherein themoisture is controlled in a range of between 8%-12% during separation,and wherein the temperature is controlled to not fall below 25° C.during separation.
 14. Application of the aleurone components separatedor isolated by the method according to claim 1 as an additive infoodstuffs or feedstock, or as a food supplement or feed supplement. 15.Application according to claim 14, wherein the food supplement or thefeed supplement is a pressed pellet of aleurone components and anutritionally and physiologically harmless binding agent. 16.Application according to claim 14, wherein the additive or the foodsupplement or feed supplement is a drink.
 17. Application according toclaim 14, wherein the additive or the food supplement or feed supplementis a powder.
 18. Application according to claim 14, wherein the foodsupplement is a starchy product.
 19. Application according to claim 14,wherein the food supplement is a dairy product.
 20. Aleurone-containingproduct containing the aleurone components separated or isolatedaccording to claim
 1. 21. Product according to claim 20, wherein theproduct is a powdered aleurone concentrate.
 22. Product according toclaim 20, wherein the product is an aleurone juice concentrate. 23.Method according to claim 1, wherein the aleurone tissues are separatedfrom the seed coat undamaged by means of a mild mechanical action. 24.Method according to claim 23, wherein the mechanical action is appliedto the bran in the form of active shearing forces.
 25. Method accordingto claim 24, wherein the mechanical action is applied to the bran bymeans of an extruder.
 26. Method according to claim 1, whereinseparation is performed by mechanical and abrasive action.
 27. Methodaccording to claim 26, wherein separation of the aleurone componentsfrom the non-aleurone components is performed in a roller mill. 28.Method according to claim 26, wherein separation of the aleuronecomponents from the non-aleurone components is performed in acentrifugal impact mill.
 29. Method according to claim 26, whereinseparation of the aleurone components from the non-aleurone componentsis performed in a jet mill.
 30. Method according to claim 26, whereinseparation of the aleurone components from the non-aleurone componentsis performed by a combination of the separation steps in claims 27through
 29. 31. Method according to claim 26, wherein the bran ismoistened before it is subjected to the mechanical abrasive treatment.32. Method according to claim 26, wherein the bran is added to water andthe aleurone components are separated from the non-aleurone componentsin a colloid mill.
 33. Method according to claim 26, wherein the bran isadded to water and the aleurone components are separated from thenon-aleurone components in a ball mill.
 34. Method according to claim33, wherein plastic balls are used in the ball mill.
 35. Methodaccording to claim 1, wherein the process is used to process wheat branand whereby the different particles of the coarse fraction of the bran,which contains both non-aleurone hull particles originating in thefurrow of the wheat kernel and aleurone particles, are electricallycharged and/or polarized due to static electricity in various waysduring their passage through the arched channel of the channel impellerair-classifier because of the particles rubbing against one anotherand/or the channel wall and they follow a path through an area subjectedto an electrical field after leaving the channel impellerair-classifier, allowing the collection of the non-aleurone hullparticles originating in the furrow at one spot and the collection ofthe aleurone particles at a second spot different from the first spot.36. Method according to claim 35, wherein the arched channel is acircular channel.
 37. Method according to claim 35, wherein the millproduct consisting of ground bran is separated by simultaneouslydirecting the mill product into an inclined, vibrating channel at onespot, whose inclination, surface roughness, and vibration are designedin such a way that the different mill product components move along thechannel at different migration speeds, which allows different millproduct fractions with more or fewer aleurone components to be extractedat different spots further along the channel at successive timeintervals.
 38. Method according to claim 37, wherein the separation ofthe mill product consisting of the ground bran by means of the channelis performed by simultaneously directing the mill product into aninclined, vibrating channel at one spot, whose inclination, surfaceroughness, and vibration are designed in such a way that the aleuronecomponents migrate to the upper end of the channel while thenon-aleurone components migrate to the lower.
 39. Method according toclaim 37, wherein the mill product is separated by sedimentation in afluid-filled container, whereby different mill product fractions areextracted at the bottom of the container as sediment layers containingmore or fewer aleurone components due to the differing sinking times ofthe various mill product components in the fluid-filled container. 40.Method according to claim 37, wherein the mill product is separated bymoving the mill product particles along an equipotential surface of aheterogeneous electrical field, which causes the mill jet or the millstream to be split into fractions containing more or fewer aleuronecomponents due to the differing dielectric properties of the millproduct particles.
 41. Method according to claim 40, wherein the jet ofmill product particles is moved by means of a laminar-flow carrier fluidflowing through an equipotential surface of the electrical field in adefined path and is thereby split by the heterogeneous electrical field.42. Method according to claim 37, wherein the mill product particlesbecome electrostatically charged by rubbing against one another and/oron part of the container and are then moved transversely to anelectrical field, which causes the mill jet or the mill stream to besplit into fractions containing more or fewer aleurone components due tothe differing electrical properties of the mill product particles. 43.Method according to claim 42, wherein the jet of mill product particlesis moved in a defined path by means of a laminar-flow carrier fluidflowing transversely to the electrical field and is then split by theelectrical field.
 44. Method according to claim 35, wherein separationis performed by a combination of the separation steps in claims 37through
 43. 45. Method according to claim 35, wherein the mill productfractions extracted are further treated with a biochemical substancespecific to each fraction.
 46. Method according to claim 45, wherein thebiochemical substance contains at least one of the enzymesbetaglucanase, cellulase, xylanase, and arabinase in a hydrated mediumwith which the mill product fractions are mixed into a hydrated mixture.47. Method according to claim 45, wherein the biochemical substancecontains at least one of the enzymes endoxylanase, beta-xylosidase,arabinofuranosidase, acetylesterase, xyloacetylesterase, and feruloylesterase in a hydrated medium with which the mill product fractions aremixed into a hydrated mixture.
 48. Method for processing bran andextracting aleurone cells, comprising the steps of: separatingaleurone-containing components from hull components in the bran bysubjecting the bran to impact and/or collision forces in a mill; sievingthe bran including separate aleurone-containing components and hullcomponents into fractions of different particle sizes including afraction having a particle size of greater than 100 μm; andair-classifying the fraction having particle sizes of greater than 100μm by channel impeller air-classification to separate thealeurone-containing components from the hull components.
 49. The methodaccording to claim 48, wherein the air-classifying step is carried outon a fraction having particle sizes greater than 100 μm and less than300 μm.